Perceptual Grouping due to Pitch and Amplitude in Hallucinating SchizophrenicsNielzén S. · Olsson O.
Psychoacoustic Laboratory, Department of Psychiatry, University Hospital, Lund, Sweden
17 subjects with a diagnosis of schizophrenia and hallucinations in their case history were compared with 16 subjects of a reference group regarding the appearance of a perception of streaming in a presentation of pitch alternating tones. One scale going up and down was used as part of a stimulus and the same scale going down and up as the other part (as distractor). The amplitude of the distractor was varied in order to make the perceptual regrouping (streaming) evident, which normally occurs when the amplitude approaches the same level in the two stimuli. Sixteen presentations were made. The subjects of the reference group began to hear the streaming after the sixth presentation and all of them heard it at the eighth. At the eleventh presentation some ceased to perceive any streaming and none heard it after the fourteenth presentation. In the schizophrenic group none showed a normal pattern. Overall, less than half of the schizophrenic probands heard a streaming when subjects in the reference group did. Amongst those who did, a few heard it early and kept hearing it to the end. Others started to hear it late and kept hearing it to the end, while a few heard it on and off. The remarkable aberrant grouping strategies among the schizophrenics are discussed in relation to current ideas on perceptual disturbances of the illness.
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